Book about a cop

Is there any book about a cop who dances on the line between good and bad while trying to justify the means with the ends? I don’t know what to compare it to I’m just thinking about the style of an old noir movie but with a much deeper protagonist whose conflict is for the most part with himself and with an ending that makes you think for days. Maybe I’m being too specific but I hope something along those lines exists

by BologaOriginal